Impairments in social functioning are one of the most common and debilitating deficits reported in many psychiatric diseases. Social behavior is a complex process that requires the dynamic orchestration of multiple cognitive processes and neural systems. During conversation, interactants must coordinate their actions, speech, and behaviors with one another in order to have efficient, effective communication. Previous research has shown that interactants automatically adapt to their partner by coordinating the timing or rhythm of their behaviors (e.g., when to talk, when to gaze) as well as the similarity of their behaviors (e.g., mimicking the facial expressions, actions, and gestures). Interpersonal coordination facilitates social affiliation, empathy, emotion processing, and communicative efficacy. Importantly, this type of coordination has been found to be impaired in many mental health disorders, including autism and schizophrenia; however the neural mechanisms that support interpersonal coordination are unknown. The proposed studies will be conducted with brain injured individuals with stable and circumscribed lesions which allows us to not only contribute to characterizing the specific brain regions necessary for interpersonal coordination, but may also contribute to new directions in the treatment of patients with mental health disorders and other complex cognitive disorders who suffer from impairments in interpersonal coordination. This proposal specifically hypothesizes that areas of the brain involved in social behavior, including the ventromedial prefrontal cortex (VMPC) and amygdala are important for mimicry of behaviors in social interaction (e.g., postures and behaviors) and for the timing of behaviors in social interaction (e.g., timing of gaze, turn-taking in speech). Additionally, it is hypothesized that mimicry of emotional expressions and experiences relies on additional structures involved in emotional processing, including right somatosensory cortex, and insula. The experiments proposed examine interpersonal coordination under increasing levels of complexity and ecological validity, from basic facial muscle mimicry of static facial expressions (e.g., the muscles involved in producing a smile become active when simply observing another's smile) and mimicry of dynamic emotional experiences (e.g., feeling happy when seeing others laughing), to examining more complex aspects of mimicry and interactional synchrony in dynamic social interactions which come closer to real-world settings than traditional laboratory experiments (e.g., mimicry of speech styles, gaze-timing, turn-taking, durations of pauses). Furthermore, the second aim of this study proposes to develop ecologically valid methods for the rehabilitation and treatment of interpersonal coordination impairments in brain-damaged individuals, which may positively influence social communication, and can be adapted for other clinical populations. Therefore, the overall goal of this project is to further inform the neural mechanisms of social behavior and contribute to knowledge of mechanisms and treatment of related mental health disorders. PUBLIC HEALTH RELEVANCE: Many mental health disorders (e.g., autism, schizophrenia, major depressive disorder) are associated with impairments in communication, emotion processing, and social functioning. The aim of this research proposal is to examine the neural systems necessary for interpersonal coordination, a process important for effective and efficient communication and emotion processing, and involves the ways in which people coordinate and adapt the timing and similarity of their behaviors during social interaction (e.g., when to talk or gaze; adopting similar postures and facial expressions). Through better understanding of the neural and psychological mechanisms underlying this important process for communication, empathy, and developing rapport, we can better inform the mechanisms and treatment of complex mental health disorders such as autism and schizophrenia.